Intrinsic subtyping of breast cancer and its relevance with clinico-pathological features and outcomes in patients from North India: a single center experience

Background: There has been a paradigm shift in the way we understand, classify, diagnose, and treat breast cancer in the last two decades, mainly due to breakthrough in the knowledge and understanding the biology of the disease. The panel of St. Gallen meeting proposed to classify tumors based on intrinsic subtypes based on the immune-histochemical pattern for therapeutic purposes. Each subtype is unique in incidence, biological behavior, survival outcome, and response to therapy. Aim: To analyze the relevance of intrinsic molecular subtypes of breast cancer with clinico-pathological features with regard to patient characteristics, disease biology, management, and outcome at 2 years follow-up. Materials and Methods: St. Gallen International Expert Consensus Recommendation 2011 was used for this study. Clinico-pathological features (age, stage of disease, histological type and grade, tumor size, lymph node status, and lympho-vascular invasion) were analyzed among the subgroups. Results: In our study, we had 64 (34.4%) luminal A, 37 (19.9%) luminal B HER2 negative, 6 (3.2%) luminal B HER2 positive, 33 (17.7%) HER2 enriched, and 46 (24.7%) triple negative breast cancer (TNBC). The disease free survival and overall survival at 2 years of follow-up was 92.2% and 100% in luminal A, 89.2% and 100% in luminal B HER2 negative, 83.3% in luminal B HER2 positive, 78.8% and 90.9% in HER2 enriched, and 71.8% and 80.4% in TNBC subgroups, respectively. Conclusion: Intrinsic subtyping with immunohistochemistry corresponds well with clinico-pathological features and outcomes. This helps in prognosticating the outcome and administration of appropriate adjuvant therapy.